Low radar observability (LO) may be a critical design requirement for certain types of aircraft, e.g., reconnaissance helicopters. To satisfy the LO design requirement, the aircraft is configured and/or fabricated to minimize the radar signature reflected to ground and/or air-based scanning/tracking radars. One method of achieving LO characteristics in aircraft is to minimize abrupt contour changes or structural discontinuities in the external surface of the aircraft fuselage. Abrupt contour changes/structural discontinuities change the electrical impedance of the aircraft fuselage which increases the cumulative aircraft signature due to reflected radar energy.
External latching mechanisms and panel/door hinge combinations for securement of aircraft fuselage panels/doors create structural discontinuities which increase the reflected radar signature of aircraft. One prior art solution for minimizing the radar signature of such structural discontinuities includes absorptive coatings applied to the latch mechanism and door hinge combination to absorb a portion of the incident radar energy. Another solution is to shape the latch mechanism and/or door hinges to minimize the amount of radar energy reflected therefrom. While such solutions are generally effective, such solutions tend to increase the overall system cost of the aircraft.
Still another solution is to provide internal latch mechanism and door hinge combinations that eliminate external structural discontinuities. Such combinations, however, may be of limited utility where internal access is required for engagement/disengagement of the latch mechanism for access panel/door opening and closure. The utility of such internal combinations is limited for many applications, e.g., equipment bays, access doors/panels, etc. that must be externally accessible.
A need exists to provide a hinge assembly for aircraft access doors/panels that eliminates external structural discontinuities in the aircraft airframe. The internal hinge should provide a swing radius that allows the access door/panel to be fully opened to provide external access. The hinge assembly should be configured and operative to preclude strike damage to the access panel during opening and closing thereof. The internal hinge should be simple to fabricate, assemble, and install, and possess a high degree of reliability.